After checking my keyboard many times and trying in many text editors and even using other keyboards, I have learned that it’s backspace and delete keys works perfectly fine. But,
for some reason, the backspace and delete keys do not work in any Desmos calculator expressions, this includes geometry, graphing, and 3D. The backspace does work perfect in folder titles and the notes though.
I’m not experiencing the same issue, but as a desmos calculator issue, it should be reported to support@desmos.com to make contact with the right team.